The use of pure iron oxide, Fe.sub.2 O.sub.3, as a catalyst in the orthomethylation of phenol has been disclosed in British Pat. No. 717,588. This catalyst exhibits a high alkylating activity even at a relatively low temperature, but its moderate selectivity for ortho-alkylation as well as relatively short operating life make the catalyst economically unattractive.
Attempts have been made to improve the properties of pure iron oxide catalysts by means of additional oxide components. Numerous catalyst compositions have become known containing, besides the primary iron oxide component, chromium oxide in particular. DOS No. 2,428,056 (British Pat. No. 1,428,057) describes catalysts having the composition Fe.sub.2 O.sub.3 /Cr.sub.2 O.sub.3 /(SiO.sub.2)/K.sub.2 O, exemplifying a metal-atomic ratio of 100:1:(10.sup.-4):2.times.10.sup.-3. A binary iron oxide/chromium catalyst is described in Published Japanese Pat. No. 76012-610 and a catalyst containing iron oxide, chromium oxide, indium oxide, silicon oxide and potassium oxide is claimed in Japanese Pat. No. 58 109 436. Furthermore, catalysts consisting predominantly of iron oxide are known having the compositions Fe/Cr/Ge (or Ga, Nb) (European Patent Publication No. 0 019 476), Fe/Cr/Ge (or Si)/Mn (or La) [German Pat. No. 3,103,839 (U.S. Pat. No. 4,227,024 and British Pat. No. 2,072,674)] as well as Fe/Cr/Sn/K (U.S. Pat. No. 4,227,024), Fe/Cr/Zr (or Cd and others)/K.sub.2 CO.sub.3 (European Patent Publication No. 0 050 937), and Fe/Cr/Ce (European Patent Publication No. 0 081 647). Thus, all of the prior art iron oxide combinations contain, as an essential component, the oxide of trivalent chromium.
In contrast thereto, industrially useful iron oxide catalysts containing, in place of the oxide of trivalent chromium, the oxides of hexavalent molybdednum or hexavalent tungsten have not been disclosed to be useful for phenol methylation. Although the above-cited U.S. Pat. No. 4,227,024 mentions a binary mixture consisting of iron oxide and molybdenum oxide (MoO.sub.3), this oxide mixture is said in the patent to be useless for phenol methylation. Also, by direct comparison of the binary oxide mixtures Fe/Cr, Fe/Mo, Fe/W under otherwise identical experimental conditions, it is found that at high total selectivity toward ortho-alkylation, a drop in selectivity toward 2,6-dimethylphenol occurs if there is a substitution of Fe oxide/Cr oxide by Fe oxide/Mo oxide and especially if there is substitution by Fe oxide/W oxide.